DIGESTIVE SYSTEM ANATOMY AND PHYSIOLOGY SUMMER, 2002

I GENERAL CHARACTERISTICS

A. PRIMARY ROLE: introduction of food for cellular absorption and utilization

1. INGESTION - eating

2. MOVEMENT - passage along GI tract

3. SECRETION - release of water, acids, buffers and enzymes

4. DIGESTIVE - chemical and mechanical breakdown

5. ABSORPTION - digested food into circulating/lymph fluid

6. DEFECATION - elimination of undigested substances

B. GENERAL ANATOMY 1. MAJOR DIVISION

a. GI TRACT (ALIMENTARY CANAL)- continuous tube with 2 openings; 30 ft.

1) Consist of mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus

b. ACCESSORY STRUCTURES - aid in digestive processes

1) Consists of teeth, tongue, salivary glands liver, gallbladder and pancreas

2. TISSUE ORGANIZATION

a. MUCOSA (Inner) - mucous membrane attached to layer of visceral muscle

1) LINING EPITHELIUM - innermost layer

2) LAMINA PROPRIA - loose connective tissue; many blood vessels and lymphatic
tissue-Mucosa Associated Lymphoid Tissue (MALT)

3) MUSCULARIS MUCOSAE -smooth muscle fibers creating many folds

b. SUBMUCOSA - dense connective tissue that binds with muscularis muscosae; highly
vascular; has Plexus of Meissners (autonomic connection)

c. MUSCULARIS - for mouth, pharynx and esophagus - skeletal muscle for voluntary
swallo wing ; rest of GI tract - smooth muscle in 2 sheets: inner ring of circular fibers,
outer sheet longitudinal fibers; has Plexus of Auerbach (autonomic connections)

d. SERSOA VISCERAL PERITONEUM (outermost) connects connective tissue and
epithelium

1) PERITONEUM - largest serous membrane; Peritonitis - inflammation of

membrane

a) Composition:

1) MESOTHELIUM - simple squamous

2) Underlying supporting connective tissue

b) Types:

1) PARIETAL P.- lines wall of abdominal cavity

2) VISCERAL P.- covers organs and forms some of their serosa

3) PERITONEAL CAVITY - potential space between parietal and
visceral peritoneum

c) Large specialized folds

1) MESENTERY - outward fold of serous coat of SI

2) MESOCOLON - outward fold of parietal peritoneum; binds LI to
posterior body wall

3) FALCIFORM LIGAMENT - attaches liver to anterior abdominal wall
and diaphragm

4) LESSER OMENTUM - arises as 2 fold in serosa of stomach and
duodenum; suspending them from the liver

5) GREATER OMENTUM - 4 layered fold in stomach serosa; contains
abundant quantities of adipose tissue and lymph nodes

II DIGESTIVE SYSTEM (DETAILS)

A. MOUTH BUCCAL/ORAL CAVITY 1. GENERAL ANATOMY Formed by: a CHECKS - lined with non-keratinized stratified squamous epithelium

b. HARD PALATE - anterior portion of mouth roof; formed by maxillae and
palatine bones: covered by mucous membrane

c. SOFT PALATE - forms posterior portion of mouth roof; lined with mucous
membrane

d. TONGUE - forms floor with associated muscles: comprised of skeletal
muscles covered with mucous membranes: consists of 2 identical half divided
by median septum

1. EXTRINSIC MUSCLES - originate outside tongue and insert into it;
moves tongue side to side, in & out; helps form BOLUS - rounded
mass of food

2. INTRINSIC MUSCLES - originate and inset within tongue; controls tongue shape
3.LINGUAL FRENULUM - midline fold of mucous membranes on tongue
undersurface; limits tongue movement posteriorly

4. PAPILLAE - specialized projections of lamina propria covered with epithelium a) FILIFORM - conical projections in parallel row on anterior 2/3 surface: contains do taste buds

b) FUNGIFORM - mushroom shaped; numerous at tongue tip;

contains taste buds c) CIRCUMVALLATE - form inverted 'V' on posterior surface;

contains taste buds

2. ADDITIONAL LANDMARKS

a. LIPS (LABIA) - fleshy fold around mouth orifice

1) VERMILION - transition zone where outer skin covering meets inner
mucous membrane

2) LABIAL FRENULUM - midline fold of mucous membrane; site where
inner surface of each lip attaches to corresponding gum

b. VESTIBULE - externally bounded by cheeks and lips; internally bounded
by gums and teeth

c. UVULA - conical muscular process hanging from soft palate; activates gag reflex

B. ACCESSORY STRUCTURES

1. SALIVARY GLANDS

a. PAROTID - under and in front of ears between skin and masseter muscle;
compound tubuloacinar type; becomes inflamed w mumps

b. SUBMANDIBULAR - beneath tongue base in posterior portion of mouth
floor: compound acinar type

c. SUBLINGUAL - anterior to submandibular: compound acinar type

d. SALIVA COMPOSITION

1) Primarily water; has solutes and organic substances, amylase and lysozyme

2) Urea and uric acid - body waste removal

3) Mucin - forms mucus when dissolved in water

4) Mucus - lubricates food

5) Lysozyme - bacteriolytic enzyme

6) Ptyalin/Salivary Amylase - initiates the breakdown of starch

2. SECRETION CONTROLS -1-1.5 liters/day
a. Entirely nervous control

1) Parasympathetic - stimulates normal levels

2) Sympathethetic - depresses its release

3) Mech: Food stimulates tastes bud receptors - Sup. and Inf.
Salivatory Nuclei - increase parasympathtic impulses

4) Smell, sight, touch and sound of food (learned behavior) initiates cortex impulse to Salivatory Nuclei

3. TEETH (DENTES)

a. Anatomy - located in sockets of Alveolar Processes of Mandible and Maxillae

1) GINGIVAE (GUMS) - covers socket area

2) PERIODONTAL LIGAMENT - fibrous dense connective tissue lines
socket anchors teeth and acts as shock absorber during chewing

b. TOOTH ANATOMY -

1) DENTIN-calcified connective tissue; major component of tooth

2) CROWN - portion above gums; Crown area covered with ENAMEL-(Ca
carbonate/Ca phosphate); Root area - covered with CEMENTUM - bonelike
substance attaches root to periodontal ligament

3) ROOT - 1 of 3 projections embedded in socket

4) NECK - constricted junction line of crown and root

5) PULP CAVITY - within crown area, filled with pulp - connective tissue, BV, nerves
and lymphatics; enclosed by dentin; has narrow extension thru roots (ROOT
CANALS)

c. TEETH DENTITIONS (SETS)

Deciduous/Baby teeth - at 6 month; 1 pair /month Permanent - at 6 years; 16 pairs

d. PHYSIOLOGY

1) Mechanical - Mastication

2) Chemical - salivary amylase (PTYALIN) - starch

3) DEGLUTITION (swallowing)

• Voluntary Stage - bolus moved into oropharynx; breathing temporarily
interrupted

• Pharyngeal Stage - bolus from pharynx into esophagus; involuntary movement

• Esophageal Stage - bolus from esophagus to stomach; involuntary movement

Deglutition Center - lower pons and medulla; where impulses are sent to control these various maneuvers

C. PHARYNX

• Conduit between mouth and esophagus

• Initiates involuntary phase of swallowing

D. ESOPHAGUS

1. Anatomy/Histology

a. Mucosa - nonkeratinized stratified squamous; contains mucous glands

b. Submucosa - loose CT, BV, nerves

c. Muscularis - 1st part striated, 2nd part striated and smooth muscle, 3rd part
smooth

d. Serosa (Adventitia) - loose CT layer not covered by mesothelium. CT merges with CT of
surrounding structures

• Upper Esophageal Sphincter - muscle regulates food passage from laryngopharynx to esophagus

2. Physiology

a. Secretes mucus and transports food to stomach

E. STOMACH

1 . Anatomy (General areas)

a. Fundus. Cardia, Body & Pylorus

b. Pyloric Sphincter - muscular gate between stomach and SI

2. Histology

a. Mucosa- large folds (RUGAE) which extend when full; lined with simple
columnar; openings into lamina propria (GASTRIC PITS); have glands
at bottom of pits (GASTRIC GLANDS)

Cells types:

ZYMOGENIC/ CHIEF - secrete pepsinogen (for protiens) and gastic lipase (

for short chain fatty acids)

PARIETAL CELLS - product HCl and Intrinsic Factor

MUCOUS - secrete mucus Gastric Juice - products from these three; 2-3L daily

ENTEROENDOCRINE/ G Cells - secrete gastrin: controls gastric juice

secretion

b. Submucosa - loose CT; connects mucosa with muscularis

c. Muscularis - 3 smooth muscle layers; outer - longitudinal, middle - circular.
inner - oblique: facilitates churning (mixing waves )

d. Serosa - part of visceral peritoneum

3 . Physiology - Mechanical and Chemical Breakdown

• CHYME - mixture of food & gastric secretion

• PEPSINOGEN - converted to pepsin by HCl

1 ) Additional contributions

GASTRIC LIPASE - limited use in adults; acts on short chain triglycerides

RENNIN - infants only; milk digestion

a. Gastric Secretion Regulation

1) Nervous - parasympathetic stimulation via X & presence of food in
stomach

2) Hormonal - presence of food

b. Stimulation for Gastric Emptying

1) Nerve impulses due to distention and presence of partially digested proteins, alcohol
and caffeine

2) Increase Gastrin secretions and vagus nerve impulses

3) Quantity of chyme SI can process ; food enters SI causing release of ENTERIC
GASTRIN by duodenum mucosa, maintaining gastric secretions

c. Inhibition for Gastric Emptying

1) ENTEROGASTRIC REFLEX - caused by food in SI, cause release of:

a) SECRETIN and GASTRIC INHIBITING PEPTIDE (GIP)- decreases gastric
secretions

b) CHOLECYSTOKININ (CCK) - decrease motility in GI tract (stomach
emptying)

d. Gastric Absorption - Except for water, aspirin and alcohol none occurs until SI.

E. SMALL INTESTINE (SI)

1. Anatomy 20’: communicates stomach with LI

a. General Area

1) Duodenum- pyloric sphincter to jejunum

2) Jejunum – middle region

3) Ileum- jejunum with ileocecal sphincter

2. Histology

a. Mucosa - simple columnar epithelium containing goblet and absorbtive cells. Muscoa
associated lymphoid tissue (MALT) throughout: has pits lined with glandular epithelium
containing Intestinal Glands – secrete intestinal juices: Paneth Cells- within glands secrete lysozyme

Surface Increasing Specializations:

• MICROVILLI - fingerlike projectjons of plasma membrane

• VILLI - projection .5-1 .0mm: have core of arteriole, venule, capillary network and
lymphatic vessel (LACTEAL)

• CIRCULAR FOLDS/PLICAE CIRCULARES - permanent ridges in mucosa

b. Submucosa - Duodenum only; has BRLNNERS GLANDS - secretes alkaline

7 mucus to neutralize chyme

c. Muscularis - outer longitudinal; inner circular; has numerous lymphatic nodules
and lymphatic tissue thru out

d. Serosa - mesothelium with basement membrane

3. Physiology

a. Movement of chyme/food

1) SEGMENTATION - localized contraction in areas containing food;
results in sloshing chyme back and forth; no forward movement

primarily type

2) PERISTALSIS - segmental contraction/relaxation of adjacent region
propelling chyme onward thru tract

b. Digestion

1) Intestinal Juices -2-3 L/day; pH 7.6; produced by epithelium lining villi for CHO

Maltase: Maltose= glucose + glucose

Sucrase: Sucrose= glucose + fructose

Lactase: Lactose= glucose + galactose

Dextrinase: disaccharides for Proteins - Peptidase for NA- nucleosidases and phosphotases for Lipids - Pancreatic Juice a) Regulated by chyme concentration; influenced by CCK and gastric secretions

c. Absorption

1) for CHO - absorbed primarily as monosaccharides into blood capillaries

• glucose and galactose - A/T

• furctose - facilitated diffusion

2) for proteins - absorbed primarily as AA into blood capillaries

3) for lipids

• short chain fatty acids ( SCFA) only - absorbed into blood capillaries by simple
diffusion

• long chain fatty acids (LCFA) and monoglycerides - use micelles via diffusion
MICELLES- temporary ferrying molecules consisting of special aggregates of
LCFA and monoglycerides. This combination allows movement into epithelial
cells of intestinal mucosa.

ENTEROHEPATIC CIRCULATION- cycling of bile salt secreted by hepatocytes setting reabsorbed by ileum and re-secreted into bile

a) LIPOPROTEINS - within mucosal epithelial cells, LCFA and monoglycerides
are resynthesized into newly formed triglycerides. These are aggregated into
globules and coated with proteins to facilitate transport in water medium.
These enter lacteal of villi - to lymphatic vessel - to thoracic duct- to left
subclavian vein - to brachiocephalic - to superior Vena Cava - to heart. Large
vesseled arterial circulation from abdominal aorta - to common hepatic artery.

HEPATIC PORTAL CIRCULATION - detours venous blood from GI organs and spleen before returning to heart.

Portal system carries blood between two capillary systems without

passing through heart first.

Hepatic portal vein formed by superior mesenteric and splenic vein.

b) Various Lipoprotein forms:

• CHYLOMICRONS- main bulky form leaving intestine. Shortly after
absorption. LIPOPROTEIN LIPASE in capillary endothelial cells of liver
and adipose tissue break these down to reform and store triglycerides

• VLDL - very low density lipoprotein

• LDL - low density lipoprotein

• HDL - high density lipoprotein

4) 90% of water ingested is reabsorted via osmosis

5) Electrolytes/Vitamins selectively absorbed via difusion except for B12 - combines
with Intrinsic Factor and AT in fleum

F. LARGE INTESTINE (LI)

1. Anatomy - 5'long; 2.3"dia.

a. CECUM - 3";

ILEOCECAL SPHINCTER - value between ileum and LI VERIFORM APPENDIX - blind vestigial sac

b. COLON - 4'

Ascending, Transverse, Descending and Sigmoid

c. RECTUM-8"

d. ANAL CANAL - 1"; opening (ANUS)

2. Histology

a. Mucosa - simple columnar; goblet cells; absence of villi and circular folds;

b. Submucosa - typical

c. Muscularis -

• Outer-longitudinal; have thickening forming compression bands (TAENIAE COLI)
series of pouches (HAUSTRA)

• Inner - circular

9 d. Serosa - part of visceral peritoneum

• Diverticulitis - pockets formed in the mucosal layer due to weakening of muscular
layer

• Colitis - inflammation of other portions of the colon

3. Physiology

a. Movement

1) HAUSTRAL CHURNING - modified peristalsis between adjacent haustrum

1) PERISTALSIS

2) MASS PERISTALSIS - major wave initiated from middle of transverse colon on;
3-4x/day

b. Digestion

1) Primarily done by resident bacteria rather than enzymatic action

2) Synthesize some Vit B complex & K

3) Colonic Bacteria

a. Vitamin Production
Vitamin K - clotting
Biotin - glucose metabolism
Pantothenic Acid — cellular metabolism

b. Imbalance causes mucosal irritation (e.g. wide spectrum antibiotics)

c. Absorption

1) Primarily water

2) FECES generation - undigested food, bacteria, epithelial cells, inorganic
salts and water

DEFECATION - elimination of feces; reflex aided by voluntary diaphragm and abdominal (sigmoid & rectum) contractions

• Diarrhea - too little time for absorption; dehydration

• Constipation- lack of water content results in impacted stools

G. PANCREAS - 5^- X 1"; tubutoacinar gland 1. Anatomy

a. Head. body and tail regions: has ducts to duodenum

b. Ducts to duodenum:

PANCREATIC DUCT - larger of 2: unites with common bile duct from liver & gallbladder & enter duodenum ACCESSORY DUCT - smaller of two